I have noticed that on some wifi connections my up & download speed sometimes becomes either extremely slow or dies all together, especially when up & down loading tcp & upd data.
I have also noticed that I can regain my bandwidth to a normal level by disconnecting and reconnecting from the network but this is a pain and suggests to me that the router supplied by the ISP is doing some packet inspection or port monitoring to provide a sanitized connection for the ley user and prevent themselves from having to serve transfer more data than they should be doing.